A temperature control device for a high purity gas analyzer

Abstract

The application provides a high-purity gas analyzer temperature control device which can simultaneously realize accurate detection and control of the temperature of eight targets. The application comprises a power supply circuit, a temperature sensor, a temperature signal conditioning circuit, a temperature signal analog-digital conversion circuit and a temperature heating control circuit. The multi-channel synchronous temperature heating control circuit based on a multi-channel time-division multiplexing PID algorithm simplifies the complex control algorithm and realizes accurate control of the multi-channel temperature. The temperature sensor, the temperature signal conditioning circuit and the temperature signal analog-digital conversion circuit form an eight-channel temperature detection unit which can simultaneously realize accurate detection and control of the temperature of eight targets. The application is applied to temperature detection and control of the high-purity gas analyzer, the chromatographic column of the chromatograph and the helium ionization detector, and has high temperature detection precision and high temperature control accuracy.

Description

Technical Field

[0001] This invention relates to the field of temperature control technology, and more specifically to a temperature control device for a high-purity gas analyzer. Background Technology

[0002] The accuracy of detecting and controlling the operating temperature of the chromatographic column in a high-purity gas analyzer directly affects the column's resolution and separation time for each component of the sample, thus impacting the analyzer's sensitivity and reproducibility. Similarly, the accuracy of detecting and controlling the detector's operating temperature directly affects the detector's accuracy in detecting trace components in high-purity gases. Therefore, inventing a high-purity gas analyzer temperature control device with both high detection and precise control is of significant practical importance. Summary of the Invention

[0003] In view of this, the present invention proposes a temperature control device for a high-purity gas analyzer, which can simultaneously achieve accurate detection and control of the temperature of 8 targets.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows:

[0005] This invention discloses a temperature control device for a high-purity gas analyzer, comprising a power supply circuit, a temperature sensor, a temperature signal conditioning circuit, a temperature signal analog-to-digital conversion circuit, and a temperature heating control circuit. The power supply circuit provides power to each circuit. The temperature heating control circuit is a multi-channel synchronous temperature heating control circuit based on a multi-channel time-division multiplexing PID algorithm, comprising a controller, a communication unit, and a heating control circuit. The controller includes an ARM processor, and the heating control circuit includes a driver ULN2803, a relay, and a heating rod. The temperature sensor measures the temperature of the instrument under test. The temperature signal conditioning circuit converts the temperature signal collected by the temperature sensor into a linear standard signal suitable for the input of the analog-to-digital conversion circuit. The circuit digitizes the input analog signal; each temperature sensor is connected to its respective signal input terminal, which is connected to its respective signal conditioning circuit. Each signal conditioning circuit is connected to the temperature signal analog-to-digital converter (ADC), and the ADC's digital interface is connected to the controller. The controller is connected to each heating control circuit. The controller, via an ARM processor, connects to the ULN2803 driver of the heating control circuit, controlling the on / off state of each relay in the heating control circuit. Each relay is connected to a heating rod, and the relay outputs a PWM signal to directly control the heating power. This PWM signal is obtained through an algorithm based on the current temperature measurement. The communication unit communicates with a host computer, which receives temperature data in real time and sets the control temperature.

[0006] The temperature sensor and temperature signal conditioning circuit each have 8 channels, and the temperature signal analog-to-digital conversion circuit is an eight-channel analog-to-digital conversion circuit.

[0007] Each temperature signal conditioning circuit is divided into a first-stage conditioning circuit and a second-stage conditioning circuit.

[0008] In the first-stage conditioning circuit, JP1, JP2, JP3, JP4, JP5, JP6, JP7, and JP8 serve as interfaces for eight temperature sensors. INxA is connected to the ground wire of the temperature sensor, and INxB and INxB1 are connected to the positive wire of the temperature sensor, where x = 0 to 7. Eight dual-isolation transmitters U1 to U8 are used for single-channel temperature signal acquisition in the field, converting the temperature change from 0 to 500℃ on the temperature sensor into a linear standard 0 to 5V voltage signal. The zero-point adjustment resistors and full-scale adjustment resistors for the eight dual-isolation transmitters are R111 to R126. Resistors R9 to R16 and capacitors C11 to C18 form eight filter circuits to filter the output signals of the eight dual-isolation transmitters.

[0009] The second-stage conditioning circuit includes eight dual operational amplifier chips N1 to N8 and resistors and capacitors. The eight dual operational amplifier chips and resistors and capacitors together constitute eight follower circuits and eight proportional operational circuits, which perform follower and voltage division processing on the output signal CHx of the first-stage conditioning circuit.

[0010] The analog-to-digital converter (ADC) circuit employs an 8-channel 16-bit charge redistribution successive approximation register-type ADC, using the ADC's internal 2.5V reference as the sampling reference. The output uses a 4-wire SPI serial communication to communicate with the controller, transmitting data and configuring functions via AD_DO, AD_SCK, AD_DI, and AD_CNV. The outputs CHIN0-CHIN7 of the second-stage conditioning circuit are connected to the input pins of the CL1689 ADC, respectively. Pins 11, 12, 13, and 14 of the ADC are digital output interfaces, connected to the ARM processor via resistor array RP2.

[0011] 5. The device as described in claim 4, characterized in that the temperature heating control circuit includes a Darlington transistor U9, eight SSR-24V solid-state relays K1 to K8, a 220V AC power interface P3, a one-time surface mount fuse F1, interfaces JP11 to JP18 for heating rods with eight heating channels, LEDs 1 to LED8, resistors R1 to R8, and capacitors C3, C7, C8, C27, C28, C29, C30, C31, C32, and C33; wherein the Darlington transistor U9 is used to boost the controller's TTL level to 24V, enabling the controller to control the closing and opening of the SSR-24V solid-state relays. Eight SSR-24V solid-state relays K1 to K8 are used to control the on / off state of the 220VL and POUTx of the eight heating channels, thereby controlling whether the heating rods of the eight heating channels are turned on. For the 220V AC interface P3, 220VL is connected to the live wire of the 220V AC power supply, and 220VN is connected to the neutral wire of the 220V AC power supply. A one-time surface-mount fuse F1 is used to prevent short circuits in the heating system from damaging the instrument. The heating rod interfaces for the eight heating channels are JP11 and JP12. JP13, JP14, JP15, JP16, J1P7, and JP18, where POUTx is connected to the live wire of the heating rod, and 220VN is connected to the neutral wire of the heating rod; LED1 to LED8 are used for visualization of PWM control heating; resistors R1 to R8 serve as voltage reducers; capacitors C3, C7, C8, C27, C28, C29, C30, C31, C32, and C33 are used for filtering and decoupling the 24V control signal.

[0012] The collector of the relay driver U9 is connected to the inverting input terminal of each solid-state relay. One end of the switching terminal of each solid-state relay is connected to the live wire of 220V AC power, and the other end is connected to one end of the heating rod. The heating rod is connected to the live wire at one end and to the neutral wire at the other end.

[0013] The temperature sensor used is a PT100 platinum resistance thermometer.

[0014] Beneficial effects:

[0015] 1. This invention includes a power supply circuit, a temperature sensor, a temperature signal conditioning circuit, a temperature signal analog-to-digital conversion circuit, and a temperature heating control circuit. Among these, the multi-channel synchronous temperature heating control circuit based on a multi-channel time-division multiplexing PID algorithm simplifies complex control algorithms while achieving precise control of multiple temperatures. It can simultaneously and accurately detect and control the temperature of eight targets. When applied to the temperature detection and control of a high-purity gas analyzer, it offers high temperature detection accuracy and high temperature control precision.

[0016] 2. In this invention, a temperature sensor, a temperature signal conditioning circuit, and a temperature signal analog-to-digital converter circuit form an eight-channel temperature detection unit. Temperature measurement employs a constant current source method. The temperature sensor is based on a PT100 sensor, the temperature signal conditioning circuit is based on a temperature isolation transmitter module, and the temperature signal analog-to-digital converter is based on a 24-bit resolution analog-to-digital converter. The weak current detector involved in the temperature heating control circuit can directly communicate with the host computer via an RS485 interface. The host computer can receive eight channels of temperature data in real time and set the control temperature. The temperature sensor uses a PT100 platinum resistance thermometer, which has advantages such as high accuracy, reliable performance, low temperature drift, and good linearity. Its measurement accuracy can be maintained above 0.1℃ for a long time, and the temperature measurement range can reach -200℃ to 650℃, meeting the requirements of high-purity gas analyzers for temperature detection accuracy and range.

[0017] 3. The analog-to-digital converter (ADC) of this invention is specifically an 8-channel 16-bit charge redistribution successive approximation register (SAR) analog-to-digital converter (ADC) with a data throughput rate of up to 250 ksps. This circuit uses the internal reference of the ADC, 2.5V, as the sampling reference. The output uses 4-wire SPI serial communication to communicate with the controller. Data transfer and function configuration can be realized between the controller and AD_DO, AD_SCK, AD_DI, and AD_CNV.

[0018] 4. The temperature heating control circuit of this invention is based on the working environment temperature measured by Pt100 platinum resistance thermometer. It uses an eight-channel heating control unit with Darlington transistors and solid-state relays as control units and a high-power AC heating jacket as the heating element. It uses a position-type PID control algorithm to control the heating process. By adjusting the duty cycle of the PWM output, it further controls the conduction and closing of the SSR-24V solid-state relay to control the heating rod, which is then converted into the heating time of the heating rod within one PWM cycle, thereby achieving precise temperature control. Attached Figure Description

[0019] Figure 1 This is a general block diagram of the temperature control device of the present invention.

[0020] Figure 2 This is a circuit diagram of the first-stage conditioning circuit of the present invention.

[0021] Figure 3 This is a circuit diagram of the second-stage conditioning circuit of the present invention.

[0022] Figure 4 This is a schematic diagram of the analog-to-digital conversion circuit for temperature signals in this invention.

[0023] Figure 5 This is a schematic diagram of the temperature heating control circuit of the present invention. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] This invention provides a temperature control device for a high-purity gas analyzer, and the overall scheme block diagram is as follows: Figure 1 As shown, the system includes a power supply circuit, temperature sensors, a temperature signal conditioning circuit, a temperature signal analog-to-digital converter (ADC), and a temperature heating control circuit. The power supply circuit provides power to each circuit. In this embodiment, both the temperature sensors and the temperature signal conditioning circuit have eight channels, and the temperature signal ADC is an eight-channel ADC. The temperature heating control circuit is a multi-channel synchronous temperature heating control circuit based on a multi-channel time-division multiplexing PID algorithm, including a controller, a communication unit, and a heating control circuit. The controller includes an ARM processor, and the heating control circuit includes a driver ULN2803, relays, and heating rods. Specifically, the eight temperature sensors are connected to signal input terminals JP1-JP8, each signal input terminal is connected to a signal conditioning circuit, the eight signal conditioning circuits are connected to the eight-channel ADC, and the digital interface of the ADC is connected to the controller. The controller is connected to each heating control circuit. Specifically, the controller connects to the driver ULN2803 of the heating control circuit through the ARM processor, thereby controlling the on / off state of the eight relays K1-K8 of the heating control circuit. The relays are connected to the eight heating rods JP11-JP18. When connected, the relay outputs POUT1-8 to output PWM signals to directly control the heating power. The PWM signals are obtained through an algorithm based on the current temperature measurement, thereby completing closed-loop control.

[0026] Preferably, the multi-channel synchronous temperature heating control circuit based on the multi-channel time-division multiplexing PID algorithm simplifies the complex control algorithm and achieves precise control of multiple temperatures. The weak current detector involved in the temperature heating control circuit can communicate directly with the host computer through the RS485 interface. The host computer can receive 8 channels of temperature data in real time and set the control temperature, which can simultaneously achieve precise detection and control of the temperature of 8 targets.

[0027] Furthermore, the temperature sensor uses a PT100 platinum resistance thermometer, which has advantages such as high accuracy, reliable performance, low temperature drift, and good linearity. The measurement accuracy can be maintained above 0.1℃ for a long time, and the temperature measurement range can reach -200℃ to 650℃, meeting the requirements of high-purity gas analyzers for temperature detection accuracy and range.

[0028] The temperature signal conditioning circuit converts the temperature signal collected by the temperature sensor into a linear standard signal suitable for the input of the analog-to-digital converter circuit according to the change amount. This device converts the temperature signal into a standard analog voltage signal of 0-2.5V according to the change amount. Each temperature signal conditioning circuit is divided into two parts, including a first-stage conditioning circuit and a second-stage conditioning circuit.

[0029] The circuit schematic of the first-stage conditioning circuit is as follows: Figure 2 As shown, JP1, JP2, JP3, JP4, JP5, JP6, JP7, and JP8 serve as interfaces for eight temperature sensors (three-wire PT100 platinum resistance thermometers). INxA (x = 0–7) is connected to the ground wire of the PT100 platinum resistance thermometer, while INxB (x = 0–7) and INxB1 (x = 0–7) are connected to the positive wire of the PT100 platinum resistance thermometer. U1–U8 are eight small-volume, dual-isolation transmitters specifically designed for single-channel temperature signal acquisition in the field. They convert temperature changes from 0–500°C on the PT100 platinum resistance thermometer into a linear standard 0–5V voltage signal. Resistors R111–R126 are the zero-point and full-scale adjustment resistors for these eight small-volume, dual-isolation transmitters. Resistors R9 to R16 and capacitors C11 to C18 form eight filter circuits to filter and denoise the output signals of eight small-volume dual-isolation transmitters, namely the 0 to 5V voltage signals INx (x = 0 to 7), into CHx (x = 0 to 7) signals.

[0030] The circuit schematic of the second-stage conditioning circuit is as follows: Figure 3 As shown, the second-stage conditioning circuit consists of eight dual operational amplifier chips N1 to N8 and resistors and capacitors. These eight dual operational amplifier chips, along with the resistors and capacitors, together form eight follower circuits and eight proportional operational circuits, performing follower and voltage division processing on the output signal CHx (x = 0 to 7) of the first-stage conditioning circuit. The follower processing acts as a buffer and isolation mechanism, reducing the impact of the first-stage conditioning circuit on the subsequent analog-to-digital converter (ADC). The voltage division processing transforms the output voltage signal of the first-stage conditioning circuit into the input signal CHINx (x = 0 to 7) suitable for the ADC.

[0031] Taking the first temperature measurement channel as an example, JP1 serves as the interface for the first PT100 platinum resistance thermometer. IN0A is connected to the ground wire of the first PT100 platinum resistance thermometer, and IN0B and IN0B1 are connected to the positive wire of the first PT100 platinum resistance thermometer. U1 converts the temperature on the first PT100 platinum resistance thermometer into a standard voltage signal IN0 between 0 and 5V. Resistor R111 serves as the zero-point adjustment resistor for the small-volume dual-isolation transmitter U1, enabling fine-tuning of the output voltage signal IN0 of the small-volume dual-isolation transmitter U1 to 0V at a detected temperature of 0℃ to eliminate zero-point error. Resistor R112 serves as the full-scale adjustment resistor for the small-volume dual-isolation transmitter U1, enabling fine-tuning of the output voltage signal IN0 of the small-volume dual-isolation transmitter U1 to 5V at a detected temperature of 500℃ to eliminate full-scale error. Resistor R9 and capacitor C11 form a filter circuit to filter out ripple and reduce noise from the output voltage signal IN0 of the small-volume dual-isolation transmitter U1. After filtering and noise reduction, the voltage signal IN0 becomes the voltage signal CH0. The second-stage conditioning circuit of the first temperature measurement channel consists of operational amplifiers N1A and N2A, along with resistors and capacitors. Operational amplifier N1A, the first operational amplifier in the dual operational amplifier chip N1, forms a follower circuit to process the CH0 signal. Operational amplifier N2A, the first operational amplifier in the dual operational amplifier chip N2, together with resistors R17 and R25 and capacitor C37, forms a proportional operational circuit to perform voltage division processing on the CH0 signal after the follower processing. R17 and R25 should be low-temperature drift precision resistors to reduce the influence of temperature and resistance noise on the detection signal. Resistor R21 and capacitor C40 also filter and reduce noise from the input signal CHIN0 of the second-stage conditioning circuit of the first temperature measurement channel. Pin 11 (output pin) OUTx (x = 0-7) of the signal conditioning circuit IB2012 is connected to resistors R9-R16. Each resistor is connected to terminals CH0-CH7 of capacitors C11-C18, and the other end of the capacitors is grounded. CH0-CH7 are connected to pin 3 (non-inverting input) of operational amplifiers N1A, N3A, N5A, and N7A in the second-stage conditioning circuit, and to pin 5 (non-inverting input) of operational amplifiers N1B, N3B, N5B, and N7B.

[0032] The analog-to-digital converter (ADC) circuit for temperature signals digitizes the input analog signal, enabling the system to perform digital processing and utilize the signal. The ADC circuit in this embodiment is as follows: Figure 4As shown. The core of the analog-to-digital conversion circuit is the analog-to-digital converter (ADC). This device uses a domestically produced 8-channel 16-bit charge redistribution successive approximation register (SAR) ADC with a data throughput rate of up to 250ksps. This circuit uses the ADC's internal 2.5V reference as the sampling reference. The output uses 4-wire SPI serial communication to communicate with the controller. Data transfer and function configuration can be achieved between the controller and AD_DO, AD_SCK, AD_DI, and AD_CNV. The outputs CHIN0-CHIN7 of the second-stage conditioning circuit are connected to pins 16, 17, 18, 19, 6, 7, 8, and 9 (input pins) of the CL1689 ADC, respectively. Pins 11, 12, 13, and 14 of the ADC are digital output interfaces, connected to the ARM processor through resistor array RP2.

[0033] The temperature heating control circuit uses the ambient temperature measured by a Pt100 platinum resistance thermometer and a position-based PID control algorithm to control the heating process. By adjusting the PWM output duty cycle, it further controls the on / off state of the SSR-24V solid-state relay to control the heating rod, which is then converted into the heating time of the heating rod within one PWM cycle, thus achieving precise temperature control. The circuit schematic of the temperature heating control circuit is shown below. Figure 5 As shown, U9 is a Darlington transistor used to boost the controller's TTL level to 24V, enabling the controller to control the opening and closing of the SSR-24V solid-state relays; K1 to K8 are eight SSR-24V solid-state relays used to control the conduction and disconnection of 220VL and POUTx (x = 0 to 7) of the eight heating channels, thus controlling whether the heating rods of the eight heating channels are turned on; P3 is the 220V AC power interface, with 220VL connected to the live wire of the 220V AC power supply and 220VN connected to the neutral wire of the 220V AC power supply; F1 is a one-time surface mount fuse to prevent short circuits in heating equipment from causing damage such as fires. JP11, JP12, JP13, JP14, JP15, JP16, J1P7, and JP18 serve as interfaces for the heating rods of the eight heating channels, with POUTx connected to the live wire of the heating rod and 220VN connected to the neutral wire of the heating rod. LEDs 1 through 8 are primarily used for visualization of PWM-controlled heating. Resistors R1 through R8 mainly serve as voltage reducers to protect the LEDs. Capacitors C3, C7, C8, C27, C28, C29, C30, C31, C32, and C33 are mainly used for filtering and decoupling the 24V control signal. Pins 11-18 (collectors) of relay driver U9 are connected to pin 1 (inverting input) of each solid-state relay. One end of the switching terminal of each solid-state relay is connected to the 220V AC live wire, and the other end is connected to one end of the heating element. The heating element's end is connected to the live wire, and the other end is connected to the neutral wire.

[0034] Taking the first heating and temperature control channel as an example, the controller inputs the temperature value of the first channel obtained by the analog-to-digital converter and the set target temperature value into the position-type PID control algorithm. The controller outputs the calculated PWM wave to pin 1B of U9 through OUT0. U9 converts the 3.3V control signal input on pin 1B into a 24V control signal, which is output to pin 1 of K1 through pin 1C of U9. K1 is closed when the PWM wave period is high and open when it is low. When K1 is closed, JP11 is controlled to heat; when it is open, JP11 stops heating.

[0035] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A temperature control device for a high-purity gas analyzer, characterized in that, The system includes a power supply circuit, a temperature sensor, a temperature signal conditioning circuit, a temperature signal analog-to-digital converter circuit, and a temperature heating control circuit. The power supply circuit provides power to all circuits. The temperature heating control circuit is a multi-channel synchronous temperature heating control circuit based on a multi-channel time-division multiplexing PID algorithm, including a controller, a communication unit, and a heating control circuit. The controller includes an ARM processor, and the heating control circuit includes a ULN2803 driver, a relay, and a heating rod. The temperature sensor measures the temperature of the instrument under test. The temperature signal conditioning circuit converts the temperature signal collected by the temperature sensor into a linear standard signal suitable for the input of the analog-to-digital converter circuit. The temperature signal analog-to-digital converter circuit further converts the input analog signal... The system is digitized; each temperature sensor is connected to its respective signal input terminal, which is connected to its respective signal conditioning circuit. Each signal conditioning circuit is connected to a temperature signal analog-to-digital converter (ADC). The ADC's digital interface is connected to the controller, which is connected to each heating control circuit. The controller, via an ARM processor, connects to the ULN2803 driver of the heating control circuit, controlling the on / off state of each relay in the heating control circuit. Each relay is connected to a heating rod, and the relay outputs a PWM signal to directly control the heating power. This PWM signal is obtained through an algorithm based on the current temperature measurement. The communication unit communicates with a host computer, which receives temperature data in real time and sets the control temperature. The temperature sensor and temperature signal conditioning circuit each have 8 channels, and the temperature signal analog-to-digital conversion circuit is an eight-channel analog-to-digital conversion circuit. Each temperature signal conditioning circuit is divided into a first-stage conditioning circuit and a second-stage conditioning circuit. In the first stage of the conditioning circuit, JP1, JP2, JP3, JP4, JP5, JP6, JP7 and JP8 serve as interfaces for 8 temperature sensors. INxA is connected to the ground wire of the temperature sensor, and INxB and INxB1 are connected to the positive wire of the temperature sensor, where x = 0~7. Eight dual-isolation transmitters U1~U8 are used for single-channel temperature signal acquisition in the field, converting the temperature change from 0~500℃ on the temperature sensor into a linear standard 0~5V voltage signal; the zero-point adjustment resistor and full-scale adjustment resistor of the eight dual-isolation transmitters are R111~R126; resistors R9~R16 and capacitors C11~C18 form eight filter circuits to realize the output signal of the eight dual-isolation transmitters; The second-stage conditioning circuit includes eight dual operational amplifier chips N1~N8 and resistors and capacitors. The eight dual operational amplifier chips and resistors and capacitors together constitute eight follower circuits and eight proportional operational circuits, which perform follower and voltage division processing on the output signal CHx of the first-stage conditioning circuit.

2. The apparatus as claimed in claim 1, characterized in that, The analog-to-digital converter (ADC) circuit employs an 8-channel 16-bit charge redistribution successive approximation register-type ADC, using the ADC's internal 2.5V reference as the sampling reference. The output uses a 4-wire SPI serial communication to communicate with the controller, transmitting data and configuring functions through AD_DO, AD_SCK, AD_DI, and AD_CNV. The outputs CHIN0-CHIN7 of the second-stage conditioning circuit are connected to the input pins of the CL1689 ADC, respectively. Pins 11, 12, 13, and 14 of the ADC are digital output interfaces, connected to the ARM processor via resistor array RP2.

3. The apparatus as described in claim 2, characterized in that, The temperature heating control circuit includes a Darlington transistor U9, eight SSR-24V solid-state relays K1~K8, a 220V AC power interface P3, a one-time surface mount fuse F1, heating rod interfaces JP11~JP18 for eight heating channels, LEDs 1~LED8, resistors R1~R8, and capacitors C3, C7, C8, C27, C28, C29, C30, C31, C32, and C33. The Darlington transistor U9 is used to boost the controller's TTL level to 24V, enabling the controller to control the opening and closing of the SSR-24V solid-state relays. Eight SSR-24V solid-state relays (K1~K8) are used to control the on / off state of the 220VL and POUTx terminals of the eight heating channels, thereby controlling whether the heating rods of the eight heating channels are activated. For the 220V AC interface P3, 220VL is connected to the live wire of the 220V AC power supply, and 220VN is connected to the neutral wire of the 220V AC power supply. A one-time surface-mount fuse F1 is used to prevent short circuits in the heating system from damaging the instrument. The heating rod interface J for the eight heating channels... P11, JP12, JP13, JP14, JP15, JP16, J1P7, and JP18, where POUTx is connected to the live wire of the heating rod, and 220VN is connected to the neutral wire of the heating rod; LED1~LED8 are used for visualization of PWM control heating; resistors R1~R8 serve as voltage step-down resistors; capacitors C3, C7, C8, C27, C28, C29, C30, C31, C32, and C33 are used for filtering and decoupling the 24V control signal.

4. The apparatus as described in claim 3, characterized in that, The collector of the relay driver U9 is connected to the inverting input terminal of each solid-state relay; one end of the switching terminal of each solid-state relay is connected to the live wire of 220V AC power, and the other end is connected to one end of the heating rod. The heating rod is connected to the live wire at one end and to the neutral wire at the other end.

5. The apparatus according to any one of claims 1-4, characterized in that, The temperature sensor uses a PT100 platinum resistance thermometer.

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